A 60-minute sequence of photos captures the asteroid 6478 Gault and its unexpected tail moving across against the starry background on Jan. 9, 2019. Damian PeachIn late October 2018, a faint asteroid named 6478 Gault suddenly brightened. Two weeks later a most curious thing happened — it grew a tail! Photos revealed a needle-thin, dust tail that extended for 248,500 miles (400,000 kilometers) — more than the distance between the Earth and the moon.In this artist illustration, dust released by an impact is focused away from the asteroid by the physical pressure of sunlight. NASASince its discovery in 1988 Gault hadn’t attracted much attention, just another faint stony asteroid in diameter minding its business in the main asteroid belt between Mars and Jupiter. What caused it to grow a tail is still unknown but there are a couple possibilities. The most talked about one is that a tiny asteroid struck it and sent a cloud of dust and rock flying away into space. The dust must be very fine, similar to comet dust, because the pressure of sunlight has shaped into a narrow plume “downwind” from the asteroid.This image depicts the two areas where most of ...